(1) Field of the Invention
The present invention relates to a device which generates normal vector information on the surface of an object, and in particular to a device which generates normal vector information from a polarized image.
(2) Description of the Related Art
It is said that mobile phones with a camera, digital cameras, digital movie cameras, and the like will be highly refined in the future as in the case of high definition televisions (HDTV), and miniaturization of these is being progressed to provide added values. However, it is conceivable that miniaturization of an optical system and imaging elements causes problems of limiting sensitivity and basic imaging performances such as the diffraction limit of a lens, and that high refinement will reach the limit in the future. In this case, the image quality can be enhanced by assigning, using computer graphics, information related to various physical characteristics used to generate an image, in addition to obtained insufficient image information of an object. For this, physical information in an image generating process must be obtained beyond the range of the conventional two-dimensional image processing. Examples of such physical information include three-dimensional shape information of the object, and a light source for lighting the object. Input of shape information requires an active sensor which projects a laser light or a LED light source, a distance measuring system such as a two-eye stereo, or the like, and thus requires a large system. This generates restrictions that, for example, it is only possible to reduce a distance between a camera and an object approximately to a few meters, and a target object must be a bright solid diffuse object. Therefore, such camera or the like cannot be used to image distant outside scenes such as scenes in athletics meets and to image portraits where hairs and clothes are important.
One of techniques which can be used to image outside scenes and general objects is a technique for using polarization as a completely passive method for sensing the shapes of objects. For example, Patent Reference 1 discloses a method for generating normal vector information of portions of an object according to a method for observing specular reflection components while rotating a deflecting plate mounted in the front of the lens of a camera without making any special assumption for lighting the object (random polarization: non-polarized lighting). The surface normal vector of the object has two-dimensional degrees of freedom determined by calculating two angles that are an angle of an incident plane containing rays of incidence light and reflected light and an angle of incidence on the incidence plane. The information of incidence plane for specular reflection is calculated from the angle at which the value of luminance changed by the rotation of the deflecting plate becomes the minimum.
For example, in Patent Reference 1, the one-dimensional degree of freedom of an angle at an emission plane containing rays of incidence light and reflected light is calculated from among the normal vector information of the object according to a method for observing diffuse reflection components while rotating the deflecting plate mounted in the front of the lens of the camera without making any special assumption for lighting the object (random polarization: non-polarized lighting). The information of emission plane for diffuse reflection is calculated from the angle at which the value of luminance changed by the rotation of the deflecting plate becomes the maximum. According to this approach, it is possible to calculate two-dimensional degrees of freedom which represent the normal vectors of an object by performing stereo processing while changing the positions of the camera and the light source.    [Patent Reference 1] Specification of U.S. Pat. No. 5,028,138    [Non-patent Reference 1] Ondrej Drbohlav and Sara Radim, “Using polarization to determine intrinsic surface properties”, Proc. SPIE Vol. 3826, pp. 253-263, 1999